The present invention generally relates to optical space switches, and more particularly to an optical space switch in which switch optical signals are spatially multiplexed. Further, the present invention is concerned with a network using such optical space switches.
Optical switches are used for switching optical signals between devices such as boards, chips, waveguides, and optical fiber cables. Currently, the speed and capacity of communication and information processing is increasing. Thus, there is a need for optical switches capable of switching optical signals at high speeds and high density. Particularly, there is a need for optical space switches which are multiplexed in the one- or two-dimensional space.
Referring to FIGS. 1A and 1B, there is illustrated a conventional optical space switch. More specifically, FIG. 1A shows the entire structure of a conventional waveguide type optical space switch which has an array of crossbar switches. The optical space switch shown in FIG. 1A has a dielectric (LiNbO.sub.3) substrate 41 having an electro-optical effect. Waveguides A1-A8-a1-a8, and b1-b8-B1-B8 are formed on the dielectric substrate 41. FIG. 1B shows an optical switch arranged at each cross point, at which four electrodes p1-p4 are arranged.
The electric fields resulting from the electrodes p1-p4 are controlled, so that the connection between the two waveguides can be controlled. For example, by controlling the electrical fields at a cross point P1, two light paths, one consisting of A1-a1 and b1-B1, and the other consisting of A1-B1 and b1-a1, are selectively obtained. In this manner, the light paths can be arbitrarily switched between inputs A1-A8 and outputs B1 and B8.
Referring to FIG. 2, there is illustrated another conventional optical space switch, which is composed of several optical elements. Polarization beam splitters 42 and 43, total reflection mirrors 44 and 45, and polarization controllers 46 and 47. Each of the polarization splitters 42 and 43 passes a horizontally polarized component of an input light and reflects a vertically polarized component thereof. Each of the polarization controllers 46 and 47 rotates the polarization direction of the input light by 90.degree. when it is turned ON. A light input 1 and a light input 2 are projected onto the polarization beam splitter 42 in the mutually perpendicular directions. The polarization beam splitter 42 divides each of the light inputs 1 and 2 into a horizontal polarization component and a vertical polarization component and emits these components to two output paths in such a way that the horizontal polarization component of the light input 1 and the vertical polarization component of the light input 2 penetrate on an identical output path. When the polarization controllers 46 and 47 are OFF, the components on the two output paths pass through the polarization controllers 46 and 47, and enter the polarization beam splitter 43 so that the components on the same path are perpendicular to each other. In the polarization beam splitter 43, the two paths, or the components thereon merge together, so that light outputs 1 and 2 corresponding to the light inputs 1 and 2 respectively are emitted therefrom.
On the other hand, when the polarization controllers 46 and 47 are ON, the horizontal polarization components are converted into the vertical polarization components by the polarization controllers 46 and 47, and the vertical components are converted into the horizontal polarization components thereby. The components from the polarization controllers 46 and 47 merge together in the polarization beam splitter 43, so that the light inputs 2 and 1 corresponding to the light inputs 1 and 2 respectively are emitted therefrom. In the above-mentioned way, the light inputs 1 and 2 are spatially switched.
Referring to FIG. 3, still another conventional optical space switch which uses polarization elements is illustrated. The conventional optical space switch in FIG. 3 has polarization separating films 48 and 49, total reflection films 50 and 51, and a polarization control element 52. In the structure shown in FIG. 3, the polarization beam splitters 42 and 43, and the polarization controllers 46 and 47 shown in FIG. 2 are integrally formed. The optical space switch in FIG. 3 operates in the same way as that shown in FIG. 2.
However, the above-mentioned conventional optical space switches have the following disadvantages. The optical space switch shown in FIG. 1 can switch optical signals between only the adjacent light paths. In order to realize a complex switching, it is necessary to use a large number of stages of optical space switches. Further, the optical space switch in FIG. 1 cannot switch light inputs arranged in the two-dimensional space.
Each of the structure shown in FIGS. 2 and 3 functions as a two-input two-output optical space switch. However, it is very difficult to implement optical space switches which handle three or more light inputs.